In conventional rotating electric machines, armature cores are formed using a laminated core, being a stack of thin plate-like steel sheets, in order to suppress generation of heat due to eddy current, logs in the armature. Armature cores are often formed using split cores, in order to enhance the production workability of the armature. In such cases, welding is resorted to as an ordinary method for connecting to each other the steel sheets of the laminated core, and to connect to each other the split cores (see for instance PTL 1 and 2).
Welding is a method that relies on a simple operation and that allows obtaining high connection strength easily and reliably. However, a problem of distortion in the armature core arises on account of the heat input into the armature core caused by welding.
The greater the overall uniformity of the facing distance (hereafter referred to as gap distance) between the magnetic pole teeth of the armature and the magnets of the rotor in the rotary electrical machine, the better are the operation characteristics obtained for instance in terms of suppression of operating vibration. In order to make the gap distance uniform, the armature and the rotor are required to exhibit a perfect circular shape, and hence it is necessary to avoid the occurrence of distortion in the armature core. In other words, distortion in the armature core caused by wielding is an underlying factor of impairment of the operation characteristics of the rotary electrical machine.
In the conventional technology disclosed in PTL 1, therefore, the positions of welding performed in order to connect to each other the steel sheets of the laminated core are distributed according to a staggered layout, to disperse heat input positions, and suppress as a result, distortion in the armature core.
In the conventional technology disclosed in PTL 2, the impact of distortion on the armature core is reduced by distributing, at regular intervals on the outer peripheral surface of the armature, a number of welding positions worked out on the basis of a relationship between the number of slots of the armature and the number of magnetic poles of the rotor.